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Migrate jsonpull to unique_ptr ownership

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Replaces the shared_ptr-based json_object_ptr with a unique_ptr that
has a stateless custom deleter dispatching on json_object::type before
calling the right subclass destructor. Eliminates per-node atomic
reference-counting and the control-block allocation that shared_ptr
required for every node in the tree.

API now distinguishes owning and borrowing pointers explicitly:
- json_read / json_read_separators / json_hash_get return raw
  json_object * (borrowed from the parser-owned tree).
- json_read_tree / json_disconnect return json_object_ptr (caller
  takes ownership; back-pointers are cleared so the subtree can
  outlive the parser).
- json_free / json_context / json_stringify take raw pointers.
- The parser's container_stack holds raw pointers; jp->root keeps
  unique_ptr ownership of the most recent top-level value.

Internally, take_from_owner moves the unique_ptr out of whichever
parent vector / hash entry / parser root owned it, which both
json_free and json_disconnect rely on.

In the streaming parsers (parse_feature, parse_layers, the
geojson-loop callback), we are careful to free `j` only after we
have processed a complete Feature: json_read returns each token
as the tree is being built up, and freeing an intermediate node
would splice it out of the surrounding hash and corrupt the
in-progress feature.

Benchmark (tl_2022_us_county.json, -z0 --extend-zooms-if-still-dropping,
median of 5 runs on macOS arm64): 8.5s, vs 10.6s with shared_ptr
and 8.7s on the pre-refactor C baseline.

Co-authored-by: Cursor <cursoragent@cursor.com>
This commit is contained in:
Erica Fischer
2026-05-30 20:44:25 -07:00
co-authored by Cursor
parent 1a7075e3ab
commit 65beb3f0d7
23 changed files with 408 additions and 289 deletions
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geobuf.cpp
+3 -3
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@@ -398,17 +398,17 @@ void readFeature(protozero::pbf_reader &pbf, size_t dim, double e, std::vector<s
json_object_ptr o = json_read_tree(jp);
if (o != nullptr) {
json_object_ptr min = json_hash_get(o, "minzoom");
json_object *min = json_hash_get(o, "minzoom");
if (min != nullptr && (min->type == JSON_NUMBER)) {
sf.tippecanoe_minzoom = integer_zoom(sst->fname, milo::dtoa_milo(min->number()));
}
json_object_ptr max = json_hash_get(o, "maxzoom");
json_object *max = json_hash_get(o, "maxzoom");
if (max != nullptr && (max->type == JSON_NUMBER)) {
sf.tippecanoe_maxzoom = integer_zoom(sst->fname, milo::dtoa_milo(max->number()));
}
json_object_ptr tlayer = json_hash_get(o, "layer");
json_object *tlayer = json_hash_get(o, "layer");
if (tlayer != nullptr && (tlayer->type == JSON_STRING)) {
layername = tlayer->string();
}